The invention relates generally to the field of civil aviation, and more particularly to a device and to a method for determining and indicating, on board an airplane, climate-relevant effects of a contrail produced by an airplane.
It is known (compare J. E. Penner et al.: “Aviation and the Global Atmosphere” IPCC, 1999, Technical Report, Cambridge University Press) that climate-relevant effects of air traffic are due, in particular, to the following three engine emission products:                water vapour (1.25 kg),        carbon dioxide (3.15 kg), and        nitrogen oxides (5-25 g).        
The above details in brackets are approximate details that state the mass of the individual combustion products with combustion of 1 kg of kerosene in modern engines in cruise flight. The climate-relevant effects of the engine emission products are as follows. Carbon dioxide (CO2) and water vapour (H2O) directly act as greenhouse gases. The reactive nitrogen oxides NO, NO2, (NOx), which themselves are not greenhouse gases, influence the formation of ozone (O3), which in turn acts as a greenhouse gas. At a corresponding ambient air temperature and humidity, the emission of water vapour (H2O) from airplane engines furthermore causes the formation of condensation trails or contrails, thus additionally influencing the local radiation balance of the atmosphere.
Contrails often manifest themselves as white “linear clouds” (linear cirrus clouds) behind high-flying airplanes. Depending on environmental conditions, a contrail can exist for several hours and can propagate in such a manner that it makes a transition to a (large-) area-shaped cirrus cloud cover. Investigations have shown that the environmental conditions required for contrail formation occur relatively rarely so that in the overall consideration of air traffic contrail formation results only in approximately 15 percent of all kilometers flown. The visual characteristics of a contrail or the cirrus clouds directly forming therefrom depend on particle emissions of the engine, on particle formation in the exhaust gas stream, and on the environmental conditions. The radiation effect of contrails is highly variable, both in time and in space. At night, contrails heat up the local atmosphere, while during the day they can also have a cooling effect at least over a dark background. The heating radiation effect of contrails can reach an order of magnitude that is comparable to that of the CO2 emitted by airplane engines. The climate-relevant radiation effect of contrails is at present neither directly recorded nor influenced by means of operative measures.
From patent specification DE 103 59 868 B3, a method and a device are known by means of which a contrail forming behind an airplane can be detected. To this effect, cameras arranged in the rear region of the airplane, which cameras point against the direction of flight and are sensitive in the visible and/or infrared spectrum, record image data. By means of suitable evaluation of the recorded image data, it is possible to determine whether contrails have formed behind the airplane. Thus on board an airplane an actual statement can be made as to whether a contrail has formed behind the airplane.
From the article by Mannstein, H., Spichtinger, P., Gierens, K., “A Note on how to avoid contrail cirrus”, ELSEVIER Ltd., Transportation Research, Part D, (2005) 10, pp 421-426, it is further known that the environmental conditions required to form contrails, in particular ice supersaturation in the atmosphere, typically occur only in atmospheric layers of little vertical extension, so that a change in the altitude of only +/−2000 ft (610 m) of an airplane flying in such an atmospheric layer reduces the probability of contrails occurring by 50%.
In the state of the art it is thus possible, on board an airplane, to detect whether the airplane generates a contrail at any given time. If a contrail is generated, the airplane can prevent contrail formation by a corresponding change in its flight altitude. With methods known from the state of the art it is, however, not possible to determine on board an airplane climate-relevant effects of a contrail generated by the airplane. In particular, it has hitherto not been possible to detect whether the contrail generated at any given time behind an airplane has an atmosphere-warming effect or an atmosphere-cooling effect.